In recent years, with the development of optoelectronics industry, the optical equipment is required to be miniature and lightweight with high performance. In order to reduce the number of lenses constituting the optical system in optical equipment, more and more aspheric lenses are applied in optical design. At present, high-precision molding is widely used for aspheric lens manufacture, which refers to press molding of glass preform under certain temperature and pressure by high-precision mould with predetermined shape, in order to obtain the final shape or glass products with optical functional surface. The aspheric lenses manufactured with high-precision molding technology usually no longer require grinding and polishing, thereby reducing costs and improving productivity.
In order to replicate the high-precision modular surface on the glass moldings during high-precision molding, the glass preform is required to be pressurized under high temperature (usually 15-40° C. above the softening point temperature of glass). At this point, shaping mould is exposed under high temperature with higher pressure. The surface layer of compression mold remains vulnerable to oxidative attack even under protection. High-precision mould is the major source of high-precision molding costs, so if mould usage does not reach a certain number, the purpose of low cost and high productivity will not be achieved. To prolong the service life of mould and reduce damage to the shaping mould by high-temperature environment, molding temperature shall be reduced as much as possible. Therefore, the transition temperature (Tg) of glass materials is required to be as low as possible.
Chromatic correction is carried out by the combination of high and low dispersion lenses in modern optical imaging system. In recent years, both high and low dispersion lenses apply optical glass with higher refractivity when aberration correction is available, which makes high-refractivity and low-dispersion optical glass become more important in the field of optical glass.
US20030032542 discloses a kind of optical glass, with refractive index above 1.80, Abbe number around 40 but transition temperature of glass over 650° C., which is not suitable to be used as high-precision molding material. Besides, U.S. Pat. No. 5,288,669 discloses a kind of optical glass with refractive index above 1.88 and Abbe number over 29, of which the disadvantage is that the glass has low viscosity and is liable to be refractory.